The recent development of high mechanical advantage actuator screw systems, in which the nut consists of a series of helical rollers surrounding the jack screw, created the need for a means to cause those rollers to rotate in phased relationship with the jack screw. The best means of doing this appeared to be the addition of a gear tooth form in the root of the screw and a mating gear tooth form on the crest of the rollers.
Initially, prototypes of such screws and rollers were produced by various multiple-pass metal cutting techniques which succeeded in proving the practicality of actuators in which the actuator screw was geared to rollers in the nut by gear tooth forms which were integral with the screw and rollers. However, such manufacturing methods required multi-pass metal cutting techniques in which the screw thread was initially cut and the gear tooth form was subsequently cut or deformed into the screw thread. Such techniques also involved difficult deburring processes after the gear teeth were cut in the second pass.
The complexity of the manufacturing operations made the cost of such actuators high and limited their marketability.
This invention is a new means of skewed-axis roll forming these combined screw thread and gear tooth form parts which has many advantages. It requires only one forming pass and that is performed in a standard cylindrical die rolling machine of the two-die or three-die type. It is high speed, allowing the combined thread/tooth forms to be produced at rates as fast as 300 inches per minutes. It is chipless, and therefore reduces material costs. Finally, because of the character of the forming operations, the parts require no deburring after the initial forming operation. In some cases it may be necessary to centerless grind the O.D. of whichever part has the involute in its root so as to produce the desired radial fit between the screw and the roller. However, this is also a high-speed operation, and, as a result, the use of this invention creates great cost savings and therefore significantly expands the market for this type of actuator.